Pairs of elements with the same number of electrons in their respective 4f orbital are

[Atomic number. Eu-63, Gd-64, Dy-66, Ho-67, Tm-69, Yb-70, Lu-71, Hf-72]

A. (Eu and Gd)

B. (Dy and Ho)

C. ( Yb and Hf )

D. ( Lu and Tm)

Choose the correct answer from the options given below :

Consider the metal complexes $\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+}(\mathrm{A}),\left[\mathrm{NiCl}_4\right]^{2-}(\mathrm{B})$ and $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right]^{2+}(\mathrm{C})$. Choose the CORRECT option by considering the number of unpaired electrons present in (A), (B) and (C) respectively and the order of frequency of absorption.

$$ \text { Consider the following molecules/species : } $$

$$ \text { The correct order of carbon-oxygen double bond length is : } $$

Consider $|x|$ is the difference in oxidation states of Mn in highest manganese fluoride and highest manganese oxide. The ions with $|x|$ number of unpaired electrons from the following are :

A. $\mathrm{Sc}^{3+}$

B. $\mathrm{Zn}^{2+}$

C. $\mathrm{V}^{2+}$

D. $\mathrm{Fe}^{2+}$

E. $\mathrm{Co}^{2+}$

Choose the correct answer from the options given below :